Carbing with a fire extinguisher

Yes you can use a CO2 fire extinguisher as beer gas, no problem, as long as you do this
1. DO NOT tamper with the extinguisher valve in any way, they are pressurized to 170 to 200 Bar.
2. You MUST use it upside down for this purpose, there is indeed a dip tube that ( when upright) will pump liquid CO2 rather than gas through the valve. After connecting the regulator and building some kind of frame to hold the assembly safely in an upside down position, then clamp the handles closed.
3. There is no such thing as 'food grade CO2' it is all the same.l know, i sell the things and have friends who work for Air Products and BOC, so CO2 from a fire extinguisher is as pure as any other source.
Hope that helps. Do bear in mind that the connection between the extinguisher and the regulator is at extreme pressure, so a proper and suitable connection capable of handling that pressure needs to be made
Happy brewing

In my region most home brewers lease a tank for a one time fee and do an exchange. I bring in my empty and swap it out for a full one. I have a 10#tank (because it would fit in my kegerator and, ya know, bigger is always better) I paid a " deposit" of $50 for the tank and about $15 for the fill. When I get it refilled, I just swap tanks. The lease makes sense because every 10 years a tank needs to be pressure tested and recertified. If you "owned" the tank that cost would be yours. If you " lease it the cost is in the refill shop. I spoke to the tech at the air gas distributor, he said some tanks had been in service for 50 years or more. If it passes pressure test, they recert, refill and put it back on the floor. Once you have your tank, you can swap it anywhere they do cylinder exchanges. The only drawback is the tanks are usually steel, usually very rusty and not something that looks "pretty" that's why I hide mine in the keezer.